This invention relates to voltage translators, and more particularly to active voltage translators for mixed-supply integrated circuits.
Several years ago, most digital integrated circuits (ICs) used a standard 5-volt power supply. More recently reduced power supply voltages such as 3.3 or 3 volts have become more widespread. As smaller transistor channel lengths are used in the semiconductor processes, smaller voltages are able to break down the transistor""s conducting channel or other parts of the integrated circuit. Thus lower voltages are need to be used for the more advanced semiconductor processes that use smaller device geometries.
Mixed-supply integrated circuits have become more common. External interfaces to other IC chips may need to operate at a standard voltage, such as 3.3 volts or 2.5 volts. Internally, the IC may use smaller-size transistors that operate at a reduced supply voltage, such as 1.8 volts. The reduced supply allows for smaller channel-length transistors to be used internally, saving space and reducing capacitive loads. Power consumption is also reduced be the lower supply voltage.
More complex mixed-supply chips may have several supply voltages. Input-Output I/O interface blocks may operate with a 2.5-volt supply, while analog blocks use a 3.3-volt supply. Core digital circuits may operate with a 1.8-volt power supply.
Complex systems may have different interfacing voltage requirements. I/O pins that connect to a Peripheral Component Interconnect (PCI) bus or other Application-Specific Integrated Circuit (ASIC) chips may use 3.3-volt signals, while pins that connect to an external memory may operate at 1.8 volts.
Circuits that can convert internal signals from one power-supply voltage to another without drawing any standby current are desirable. Such voltage translators are useful to convert 3.3-volt signals from an interface block to 1.8-volt signals to the core circuits, and to convert 1.8-volt core signals to 3.3-volt signals to the interface blocks. Such voltage translators are useful for converting other signals among a variety of voltage levels.